Add Extension to Live Birth Compositions to reference maternity Encounter

Composition.encounter is limited to a maximum of 1 encounter, however a Live Birth spans two encounters - the Birth Encounter and the Maternity Encounter. The two Live Birth Compositions have the Birth Encounter as the one encounter referenced. Pilot implementers have requested that we add an extension to these Compositions to reference the Maternity Encounter to allow them to more easily get to the data in that Encounter.

Add to Composition - Provider Live Birth Report and Composition - Jurisdiction Live Birth Report an extension (must support and 0..1) that references the Maternity Encounter.